The cleansing of exposed in vivo tissue, such as of humans or animals during surgical procedures, requires the removal from the tissue of solid contaminants, such as fibers, dust, sand particles, and the like, and organic matter, such as puss, fats, and so on. Organic matter tends to be fastened to the tissue much more strongly than the non-organic matter, and is thus more difficult to remove therefrom. Accordingly, while non-organic matter may be cleansed from the tissue by means of a liquid stream, it is often not possible to remove some organic matter in this way. More specifically, and most problematic, are those particles which are smaller than the thickness of the boundary layer of the fluid stream which is formed on the tissue; the boundary layer being characterized by having a fluid velocity which reduces sharply adjacent to the flow surface, and which is zero at the surface.
The smallest particles, which are located in the boundary layer, exhibit drag resistance of a magnitude that is sufficient for them to stay affixed to the surface and not to be swept away by the fluid stream, even if this has a very high velocity.
In an attempt to solve this problem, there have been developed a number of prior art devices which employ pulsed washing streams, such as described in U.S. Pat. Nos. 4,350,158 and 4,982,730. These pulsed stream devices operate on the basis of providing a liquid stream with a reduced boundary layer thickness, in order to sweep away small particles. These devices, however, generally have complicated constructions, use very large quantities of liquid, and have been found to provide only a small improvement over non-pulsed devices.